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Current-and Voltage-Clamp Experiments in Virtual …For the following experiments, chose a voltage...
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SimNeuron Tutorial
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SimNeuron
Current-and Voltage-Clamp Experiments in Virtual Laboratories
Tutorial
Contents:
1. Lab Design
2. Basic CURRENT-CLAMP Experiments
2.1 Action Potential, Conductances and Currents.
2.2 Passive Responses and Local Potentials
2.3 The Effects of Stimulus Amplitude and Duration.
2.4 Induction of Action Potential Sequences
2.5 How to get a New Neuron?
3. Basic VOLTAGE-CLAMP Experiments
3.1 Capacitive and Voltage-dependent Currents
3.2 RC-Compensation
3.3 Inward and outward currents.
3.4 Changed command potentials.
3.5 I-V-Curves and “Reversal Potential”
3.6 Reversal Potentials
3.7 Tail Currents
4. The Neuron Editor
5. Pre-Settings
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1. Lab Design We have kept the screen design as simple as possible for easy accessible voltage- and current-clamp
experiments, not so much focusing on technical details of experimentation but on a thorough
understanding of neuronal excitability in comparison of current-clamp and voltage-clamp
recordings.
The Current-Clamp lab and Voltage-Clamp lab are organized in the same way. On the left hand side,
there is a selection box of the already available neurons with several control buttons for your recordings,
including a schematic drawing the experimental set-up. The main part of the screen (on the right) is
reserved for the diagrams where stimuli can be set and recordings will be displayed.
Initially, you will be in the Current-Clamp mode where you will only see a current-pulse (in red) in the
lower diagram while the upper diagram should be empty. Entering the Voltage-Clamp mode you will
find a voltage-pulse in the upper diagram (in blue) with an empty lower diagram. The here displayed
recordings (action potential in the current-clamp lab and currents in the voltage clamp lab) will only
appear after pressing the “Apply Stimulus” Button.
A band of several buttons gives access to additional information, e.g, to open this tutorial directly from
the program, or allows changing program pre-“settings” (not possible for demo versions). Especially, you
have the possibility to “SAVE” your recordings as graphic files on your hard disk
The Neuron Editor shows on the left
hand side a cartoon of the membrane
with the equivalent circuit and the
complete set of the model equations.
In the mid part, all parameters values
of the model are shown in text edit
boxes and can be modified to examine
their effects on the current- and
voltage-clamp recordings. The
modified neurons can be saved under
a new name.
In the graphics on the right hand side
the impact of some parameter changes
on dynamically relevant model
features can directly be observed.
Initially, you will find a “Standard
Neuron”. However, you can modify
the parameter values to examine their
impact on and can save the neuron
under a new name.You may create
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2. Basic CURRENT-CLAMP Experiments
some basic experiments with only a few mouse-clicks:
To follow these experiments, please, make sure that you are in the current-clamp mode which means that the
current-clamp button should be activated (yellow). Initially, “STANDARD NEURON” will be selected and you will
find on the right hand side in the lower diagram a current pulse (in red).
2.1 Action Potential,
Conductances and Currents.
Use the initial settings (5 nA, 0.4 ms)
and just click on the “Apply Stimulus”
button.
An action potential should appear (Fig.
1.1.1, upper diagram in blue).
In the virtual lab it is possible what
cannot be done in the real experiment,
to record simultaneously with the
membrane voltage also the time course
of ionic conductances and currents. For
that, you just have to activate the
check-boxes for gNA gK as well as
those for I_Na I_K above the diagrams.
With next click on “Apply Stimulus” also the ion conductances (in the upper diagram) and the ion
currents (in the lower diagram) will be plotted (Fig. 1.1.2), in violet for Na and green for K ions.
In the upper diagram you can see
what you know from conventional
text-book illustrations, namely that
the upstroke of the AP is related to
the fast regenerative increase of the
Na-conductance (violet) followed by
the down stroke, including after-
hyperpolarization, due to the delayed
opening of K channels (green)
combined with the inactivation of Na
channels
In the lower part the corresponding
changes of the voltage dependent Na
and K currents can displayed which
you can plot together with their leak
currents (incl. I_L), Additionally can
the sum of all currents (SI) cab be displayed
Question 1.1: Can you understand the differences in the time course of ionic conductances and currents,
e.g. why the Na-current transiently decreases (arrow) or why the K-currents is almost back to zero when
the K-conductance is still relatively high?
Hints: use Ohms Law but don’t forget to consider the “driving force”.
Go to the “voltage-clamp experiments” for a better understanding (see below).
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2.2 Passive Responses and Local Potentials
For the following experiments you should know the meaning of diverse control buttons and learn how to
change stimulus-parameters and diagram scaling:
Change STIMULUS parameters:
Amplitude and the onset of the pulse can be modified with click on the top or upward deflection of the
pulse whereby an up-down or left-right arrow, respectively, will appear. Additionally, the complete
pulse can be shifted in time with right mouse click between onset and offset of the pulse.
Change PLOT parameters (diagram scaling):
Click on one of the numbers in the boxes at the coordinates (voltage, current or time) and select the
desired range. Please note: All scaling changes will delete previous recordings. For the following experiments, chose a voltage range between –80 to +30 mV instead of –120 / +80) and, for the
current stimulus, –10 / +10 mV instead of -20 to +20 nA. Time resolution is unchanged.
Figure 1.2. shows again the action potential as
plotted above - in this case without the ion-
conductances and -currents (the corresponding
check-boxes are deactivated). Instead, the SAVE
button has been activated to keep this recording on
the screen for comparison with a purely passive
response and local potentials.
Passive Response: When the active, i.e. voltage-
dependent currents are blocked with application of
the Na+-
and K
+ -channel blockers “TTX” and
“TEA” (activation of the corresponding buttons)
only a so-called passive response remains. The
voltage change reflects the charging and discharging
of the membrane capacitance by the externally
applied current.
Supplementary Experiments with TTX and TEA application: a) Change the strength and duration of the stimulus to see the full charging of the membrane up to the
steady state (when a constant potential is reached) and determine the membrane time constant.
b) Do the same experiments when only TTX is applied and explain the differences.
c) Go back to a short, slightly subthreshold stimulus pulse and compare the action potential with a second
one after TEA application. Can you explain why the action potential develops faster and last longer?
Local Potentials: Try to adjust the stimulus amplitude to a subthreshold value which nevertheless
induces potential changes that are bigger than a pure passive response. These so-called “local potentials”
develop under contribution of active currents but are still too small to generate an action potential that can
be propagated. Physiologically, local potentials mostly appear in form of synaptic potentials due to the
opening of transmitter gated channels.
2.3 The Effects of Stimulus Amplitude and Duration.
When you have tuned the amplitude of the short stimulus of 0.4 ms to a
subthreshold value, e.g. from previously 4 nA to 3.5 nA and then increase
the stimulus duration, e.g. to 0.6 ms, an action potential again should be
elicited due to further depolarization during the additional time which also
explains the slight delay.
When you determine the threshold for AP-generation for different
combinations of stimulus amplitude and duration you will get the so-called
strength-duration-curve with the key rheobase and chronaxie.
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Action Potential Sequences
With a sufficient long duration of a supra-threshold stimulus a series of action potentials can be
generated and you also can see how the stimulus amplitude is encoded in the action potential
frequency (firing rate, rate code).
Scaling:
Please note: For these recordings, the
time-base has been expanded, here to 50
ms recording time.
To adjust the recording time click on the
maximum value at the abscissa. The
same can be done for the adjustments of
the current and voltage range with click
on the maximum values at the ordinates
(see circles)
This figure is composed from three
recordings with long lasting stimuli (40
ms) of different amplitudes.
A stimulus strength of 1nA only elicits a
slight, local response while the 2nA
stimulus generates 6 APs within the
given duration and the 8 nA leads to an
almost doubled frequency of AP
generation..
Additional experiments:
a) You can systematically increase the stimulus amplitude to determine the frequency – stimulus
curve.
b) Compare the responses of the given “Standard Neuron” with another neuron that you may
take from your neuron list, if available, or generate yourself.
2.4 How to get a New Neuron?
You can go to the neuron Editor (see
below) to modify the neurons parameter
values and save the neuron with a new
name.
Alternatively, a right mouse click into the
schematized recording arrangement (see
arrow) will offer a new neuron which will
appear in your list of neurons under a
randomly generated number (see circles).
Please note: these neurons have random
parameter settings. In the given example
the new neuron remains subthreshold
when the same stimulus is applied which
in the Standard neuron elicited a series of
APs.
right mouse click
Please note: Depending on the pre-settings, the new neurons may be subjected to “noise”.
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3. Basic VOLTAGE-CLAMP Experiments
3.1 Capacitive and Voltage-dependent Currents during a Voltage-Clamp Pulse
Go to the voltage clamp lab with click on the “VOLTAGE CLAMP” button. Now you will find a
voltage pulse in the upper diagram which you can change in the same way as the current pulse in the
current-clamp lab.
For the moment, just click on
“APPLY STIMULUS”.
A typical current curve will
appear in the lower diagram:
1) There is a brief upward and
downward deflection at the
beginning and the end of the
pulse which reflects the
cpacitive currents that are
necessary to charge and
recharge the membrane
capacitor, i.e. to bring the
membrane voltage to the
desired values (to the
command potential and back
to the holding potential).
2) In between, there is a
downward deflection which turns into an upward deflection (about 1ms after the stimulus onset). These
are the currents which are necessary to compensate for the active, i.e. voltage dependent membrane
currents to keep the potential at the desired value.
Please note: a downward deflection reflects an inward membrane current
and an upward deflection an outward membrane current.
3.2 RC-Compensation
The textbooks mostly show
recordings where the capacitive
currents are eliminated. You can
do this here – much easier than in
the real experiment – with click on
“RC-compens” (the only button
which does not have a counterpart
in the current-clamp lab).
What remains is the transient
downward deflection (inward
current) that turns into the ongoing
upward deflection (outward
current).
These are the currents of main interest because these are the “active” currents that develop due to the
voltage-dependent opening and closing of ion channels.
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3.3 Inward and outward currents.
Also in the voltage-clamp lab you can separately plot
the Na+ (violet) and K
+ (green) conductances (in the
upper diagram) and currents (in the lower diagram)
when you activate the corresponding check-boxes
above the diagrams.
In the lower diagram, you can see that the whole cell
current (in red) is the result of a fast transient (Na+)
inward current and a delayed but sustained (K+)
outward current.
3.4 Changed command potentials.
Typical voltage-clamp experiments are done with
application of a “family” of voltage stimuli with
systematically changed command potentials.
With only a few voltage stimuli as shown in the figure
it can be demonstrated that the amplitude of the
outward current continuously increases while the
maximum value of the inward current first increases,
then decreases and finally completely disappears
3.5 I-V-Curves and “Reversal Potential”
Such experiments are generally done to determine the
current-voltage (I-V) curves for specific types of ion
channels when other types of channels are blocked. In
the given examples, Na-currents have been recorded
while K-currents were blocked by TEA.
Again, you can see that this type of Na+
current is
inactivating and also that the amplitude of the current
is non-monotonically related to the command voltage,
even changing its direction from an inward to an
outward current.
Back to Question 1.1 with the observation that the Na+-
current transiently decreases during the peak of the action
potential (Fig. 1.1.2) Can you now understand why this
happens and also why the K+-current is almost zero during
the after-hyperpolarization although the K+-conductance is
still rather high?
I-V- curves are constructed by plotting the maximum
currents vs. the command voltage. Examples for both
Na+
and K+ -currents are given in the right lower
figure.
At sufficiently high voltages a linear relation appear
indicating that the maximum conductance has been
reached. The current then only depends on the driving
force. Deviations from these linear I-V relations mean
that part of the potentially available ion channels are
closed. From the relation between the measured
current and the current which would be expected when
all channels were open, according to the linear curve,
the activation curve can be constructed.
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3.6 “Reversal Potentials”
The voltage at which the current changes its direction is called the reversal potential. For Na-
currents, as shown in the examples above, is this the case at around 50mV. Here, the Na+-
current is zero although the maximum number of Na-channels should be open. The reason is
that, at this point, the “driving force” (V-VNa) becomes zero. For specific ion channels which
are selectively permeable only for one type of ions, this happens at their equilibrium potentials,
given by the Nernst equation.
Question: What would be the reversal potential for nonspecific cation channels that let pass
monovalent cations like Na and K equally well?
Reversal potentials are indicative for the type of ion channels and therefore are key values of
voltage-clamp recordings. They can be determined by the zero crossing points of the I-V curves
which for K-currents requires the elongation of the linear part of the I-V curve.
Moreover, for Na-currents the reversal potential can directly be determined by depolarizing
voltage steps in search of the point of zero current in between inward and outward directed
currents.
For K currents the reversal potential should be located below the resting membrane potential.
With current steps in hyperpolarizing direction, however, these type of K-currents will always be
zero, because these type of ion channels will keep closed.
Determining the reversal potential of K-currents, therefore requires a different strategy, namely
the recording of “tail currents”.
3.7 “Tail Currents”
Tail currents appear at the end of a
voltage step due to the delays also
of ion channel closing – provided
that a driving force unequal zero
exists. At the resting membrane
potential, this should be the case
for both, Na and K currents.
Hence, to determine the reversal
potential for K-currents it is
necessary to elucidate the voltage
where the tail current disappears.
For that, instead of changing the
command potential you can
change the holding potential, as
shown in the figure. With blockade
of Na currents the tail current
becomes zero at the K equilibrium
potential.
Questions:
a) Can you explain why the above shown tail currents would not be significantly different without
blockade of the Na currents?
b) Why can a reversal potential for non-specific ion channels for Na and K currents be found but not a
common reversal potential for both types of ion channels?
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4. The Neuron Editor The neuronal responses in the SimNeuron labs are the result of numerical simulations. The “Neuron-
Editor” provides the possibility to change the values of all model parameters to examine their impact on
the neurons’ responses in the current- and voltage-lamp lab.
You can go to the Neuron Editor from both labs with click on the corresponding labeled button.
Depending on the pre-settings (see below), the access may be password protected.
In the left upper corner you will find the list of neurons that already have been generated and saved. At
the beginning, you will only find the Standard Neuron. You can select one of the available neurons to
change its parameter values and then can go “to the lab” to check its responses. As long as the modified
neuron is not yet saved its name will appear with the extension *test*. You can “Save” your new neuron
under the same name (prohibited for the “Standard Neuron”) or under a different name. Likewise,
selected neurons can be “Deleted”. “Cancel” will bring you back to the lab without considering any
changes since the last entering of the Neuron Editor.
Below these edit boxes, there is a simple sketch of the membrane with ions and ion channels together
with the corresponding electric equivalent circuit. Below, the complete set of Equations is given.
The mid-part shows the numerical values of all membrane parameters, adjustable by text-edit boxes.
The diagrams on the right are for graphical illustrations of some functionally relevant characteristics.
The most upper text edit boxes indicate the diameter and membrane capacitance of the selected neuron.
The following text-edit boxes (“Membrane Settings” with “Ion Concentrations and Equilibrium
Potentials”, “Leak Conductances and Leak Voltages”) are related to the so-called passive membrane
properties. which, in computer modeling studies, are mostly represented by a single term for a leak
current IL = gL *(V - VL), thus only depending on a generalized leak conductance gL and the driving force
(V - VL). “SimNeuron” allows to separately adjusting the major leak conductances and also their
equilibrium (Nernst) potentials, the latter indirectly with alterations of the ion concentrations as the
physiologically relevant parameters. The effects of such parameter changes can directly be observed in
upper right diagram labeled “Leak Currents”.
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In the lower part, the numerical parameters of the “Voltage-Dependent Ion-Currents” are given
according to the equations on the left. The thereby induced alterations of the voltage and time-
dependencies of the variables m, n, and h can be observed in the corresponding graphs on the right
Two additional check boxes allow to add and to adjust a “noise” current in adjustable intensity D or to
display in addition to the control potential VC also the real membrane potential VM (in voltage-clamp
mode).
4.1 Comparison of Membrane Parameters
It has been taken care that all neurons for experimentation in the SimNeuron laboratories will initially be
in a steady, i.e. exhibiting a stable membrane potential. Indeed, new generated neurons will have random
parameter settings, however within an accordingly adjusted range. The reason is that you should have the
possibility, as one of the first tasks, to determine the threshold of action potential (AP) generation. Indeed,
you will see that the required current strength can be significantly different.
Indeed, the leak potential VL is on an almost 10mV more depolarized level (-60.5mV vs. -70.1mV).
However, also the leak conductance gL, stabilizing the membrane potential, is much higher (almost by
the factor 2.5) what also can be recognized in the steeper I-V lines of the Leak Currents. Especially, the
diameter d of the neuron is almost twice as big which leads to a membrane capacitance C that is by a
factor 2.66 bigger than that of the standard neuron. Charging a bigger conductance needs more current.
Also the parameters of the voltage dependent currents are significantly different. The maximum
conductances g for both Na+- and K
+-ions are around 4 times bigger. These, however, are mainly of
The examples compare the Standard
Neuron (SN) with a neuron of random
parameter settings. Current injection of
5nA which induces an AP in the SN
leads in the second neuron to an only
slight depolarization. Here, an almost
8 nA stimulus pulse of the same
duration is required to generate an AP,
although it is in a more depolarized
resting state.
Finding out the possible reason for the
higher threshold you can go to the
Neuron Editor to compare the
parameter values. .
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relevance for the size of the action potential in relation to the membrane capacitance to be charged and
discharged within a given time. The time constants are apparently not significantly different. Also the
voltage dependencies seem to be quite similar, therefore not so much contributing to the increased
threshold of AP generation. Likewise, differences in the ion concentrations, determining the
equilibrium potentials, may not play a significant role.
Hence, is this example it seems mainly to be the so-called passive membrane properties (capacitance and
leak conductance) that are responsible for the increased threshold of spike generation. In other examples
it could likewise be voltage dependent currents or the ion concentrations. This can be examined with
selective alterations of specific membrane parameters.
4.2 Alteration of Membrane Parameters
We are using the Standard Neuron with its defined parameter settings to illustrate the potential impact of
some specific membrane parameters on the neurons’ excitability.
4.2.1 Shift of voltage dependent activation of Na+ currents – creating a pacemaker neuron
The relation between the activation range of Na+ and K
+ currents and especially their relation to the leak
potential are exceptionally sensitive parameters in determining the neurons’ excitability. For example,
shifting the half activation potential Vh for Na+ channels slightly to more negative potentials (from 22mV
to 28mV, see red circle in the figure inset) has dramatic effects. This turns the Standard Neuron with a
stable membrane potential into a pacemaker cell which isrepeatedly generating APs, even without any
external stimulus. The stimulus pulse at the beginning, overlapping with a spontaneously generated AP,
does no play a role. For better illustration of the repetitive activity, the recording time in the figure below
has been expanded to 50ms.
4.2.2 Increasing the external K+ concentration - via pacemaker activity into a depolarization block
####
Similar effects, changing a silent neuron into a pacemaker, can be achieved in several different ways. One
more example is given below by increasing the external K+-concentration. The first, direct effect is a
reduction of the K+ equilibrium potential. This is accompanied by a likewise reduced leak potential. The
dynamically relevant effect is the same as before: The Na+ activation curve and the leak potential are
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5.0 mMol/L
20 ms
7.8 mMol/L
23.4 mMol/L
coming closer together. Spontaneous activity appears when sufficient Na+ current is activated for
regenerative depolarization already at the level of the leak potential.
Changing external ion concentration is widely used practice in
experimental research. Increasing the extracellular K+ -
concentration is common practice even in clinical situations, e.g.
bringing the heart into a depolarization block for surgery. The
same happens in neurons with sufficient high K+ concentrations
leading to sufficient depolarization. When the membrane cannot
repolarize, the Na+ channels will keep in the inactivated state.
The examples on the right show, in the upper trace, the original
situation with 5.0 mMol/L external K+ concentration where the
neuron is in the steady sate but can be excited by an external
current stimulus (arrow). With 7.8mMol/L the neuron is
sufficiently depolarized for spontaneous AP generation. With
23.4 mMol/L, still much less than the intracellular K+-
concentration of 150mMol/L, the neuron keeps depolarized at
approximately -40mV where most Na+ channels already are inactivated. The remaining ones can only
induce a tiny AP that will completely diminish with further depolarization by further increased K+
concentration
4.3 Introducing Randomness: Noise Current
All experimental recordings are contaminated by certain randomness. Apart from the diversity of the
neurons, also the same neuron will never react in exactly the same way even on completely identical
stimuli. Indeed, there will be not much difference when very strong supra-threshold stimuli are applied.
However, in the neighborhood of the threshold of AP generation, tiny random fluctuations may be
sufficient to decide whether an AP is generated or not. In reality, such randomness may be of different
origin. Here, as in most modeling studies, it is introduced by a noise current accounting for random
fluctuations over time.
The initially set stimulus values (5nA, 4ms) seem to
be just above the AP generating threshold for the
Standard Neuron. On repeated application of this
stimulus you will always find exactly the same time-
course of the action potential. With a slight reduction
of the stimulus strength to 4.8nA an action potential
will never appear (see examples on the left).
These are completely deterministic situations as you
only will find them in mathematics or with computer
simulations – but never in real life.
The recordings on the right are obtained with addition of a tiny noise current (D=0.01). Four out of ten
previously subthreshold stimuli have then been generating an action potential.
The second example illustrates, again with the
Standard Neuron, the induction of spike activity of
increasing firing rate in response to a
deterministically clearly subthreshold stimulus -
simply by addition of noise of increasing noise
intensity D.
Indeed, with sufficiently strong noise spiking can
even be induced without an additional current
stimulus.
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4.4 SAVE your own Neurons
When you have changed a parameter of one of your neurons the neurons’ name will appear in
the selection box with the extension *test* - what here is shown with an example from the
Standard Neuron (on the left) what usually will be the first step. You can go the current or
voltage clamp lab to check the effects of the parameter changes.
In case that you want to save your Standard Neuron with the altered parameter values you have to type in
another name, here “Pacemaker Na Shift” (according to the changes made in 4.2.1). The parameters of
the Standard Neuron cannot be changed.
In case that you have changed the parameters of any one of your other neurons you will be asked whether
this neuron shall be replaced by the new one or whether you want to save it under a different name.
In any case, after pressing the SAVE button, the new neuron will appear as the actually activated neuron.
in the selection box.
Please note: The parameter files of all neurons in the list will be saved with the extension “.VAR” in a
specific folder “sim-original”. With all more recent Windows versions (Vista, Win7 and Win8) you will
find the folder “sim-original” in "C:\ProgramData\Viphy\SimNeuron II\Files\". If you cannot see the
folder "C:\ProgramData\ in your Windows Explorer you have to type in "C:\ProgramData” in the address
field of your Windows Explorer.
In Windows XP your “sim-original” folder will be located in C:\Program Files\Viphy\SimNeuron
II\Files\" (in German: C:\Programme\Viphy\SimNeuron II\Files\").
If too many neurons have accumulated you can go “sim-original” to manually delete undesired neurons
from the neurons list.
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5. Pre-Settings
SimNeuron versions 2.3 and higher offer the possibility to select to which specific features of the program
your students shall have access. This can be done in so-called pre-settings window which you can open
from the labs via the SETTINGS button in the switch bank. The access to the pre-settings is password
protected. The initially set password is “admin”. You can change the password from the pre-settings
window, clicking on the password button.
Pressing the SETTINGS button and entering the correct password opens a window as shown in the figure
below. There you will find a list of different features to which you can give access (“Yes”) or which you
may protect (“No”). The presetting in this figure are those as initially set. On the right, additional
explanations to each point will appear as shown here for the last point. Explanations to the other points
are given below.
SimNeuron-Presettings:
1) Open the lab with a randomly generated neuron?
Here you can decide what kind of neuron will appear on program start. If "Yes" is selected you or your students will
get a neuron with randomly chosen parameter values. Selecting "No" will open SimNeuron with the "Standard
Neuron" which always will be the same and cannot be changed.
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Please note: You will in any case have access to the “Standard Neuron which will appear on the top of your list of
neurons in the drop down menu opening with click on the current neuron’s name.
2) Allow receipt of randomly generated neurons?
When this switch is set to “Yes” you can get additional neurons with random parameter values clicking with the
right mouse button on the schematic drawing of the experimental set-up in the lower left corner of the labs. If this
switch is set to “No” the possibility receiving new neurons is blocked.
3) Randomly generated neurons with noise?
selecting “Yes” means that randomly generated neurons include a noise term. This is not only to let the recordings
appear more realistically. Also threshold of action potential generation and spike timing will exhibit some
variability. For deterministic simulations with exactly reproducible reactions on identical stimuli, this switch should
be set to “No”.
4) Allow access to the “Neuron Editor”
In case that this switch is set to “Yes” you or your students, respectively, will be able to open the “Neuron Editor”
via the corresponding button in the SimNeuron voltage- and current-clamp laboratories. Selecting “No” blocks the
access to the “Neuron Editor”.
The “Neuron Editor” shows the full equations and all parameter values of the current neuron. It also allows
changing the neuron parameters thereby generating new neurons with different properties that can be saved in the
current list of neurons.
5) Overtake new neurons into the pre-settings list?
If this switch is set to “Yes”, new neurons that have been generated during the current session will be overtaken into
the list of preset neurons to appear in the next session. If the switch is set to “No”, new generated neurons will be
deleted on program exit so that the original list of neurons will be preserved.
Of course, this switch is only of relevance when one or both of the switches above (receipt of randomly generated
neurons or access to the neuron editor) are activated.
Additional note: If too many neurons have accumulated you can manually delete undesired neurons from the
neurons list. You will find the list of neurons in the subfolder “sim-original”.
Attention: In Win Vista, Win7 and Win8 this subfolder is NOT located in "C:\Programme\Viphy\SimNeuron
II\Files\" (due to restricted access) but in "C:\ProgramData\Viphy\SimNeuron II\Files\". If you cannot see the
folder "C:\ProgramData\ in your Windows Explorer you have to type in "C:\ProgramData\.
6) Allow to display conductances
Selecting “Yes” will bring a check box on the screen in both the current- and voltage-clamp lab which can be
activated also to display the time course of Na and K conductances – which, of course, cannot directly be seen in
real experiments. On “No” this option is blocked and the check boxes will not appear.
7) Allow to display currents separately
If “Yes” is selected check boxes will appear which allow to display the voltage dependent Na and K currents
separately. This will not be possible when the switch is set to “No”. Then, the check boxes will be hidden.
8) Show Reset Button (Initial Settings)
On “yes” a button will appear in the right upper corner which allows reinstalling the initial settings (scaling and
stimulus adjustments as after program start).
9) Allow switching to current ramps
On “yes”, in the current-clamp lab two buttons will appear in the right lower corner of the current display which
allow to switch from conventional step-like current injection to ramp-like current stimuli, e.g. to examine eventual
accommodation effects.
Buttons:
Password: opens a window to change the password
Cancel: closes the pre-settings without considering currently made changes
OK: overtake the changes for the current experiments
SAVE: preserve the changed pre-settings also for the next program start